The present invention relates to an information-processing apparatus, an information-processing method and a recording medium. More particularly, the present invention relates to an information-processing apparatus, an information-processing method and a recording medium of a transcoding system that allow information to be transmitted in such a way that necessary information can be extracted from the transmitted information with ease in dependence on the degree of information importance, and allow information to be read out from the information-recording medium wherein the picture quality does not deteriorate even if decoding and encoding processes are carried out repeatedly to modify the structure of an encoded bit stream completing an encoding process based on an MPEG (Moving Picture Expert Group) standard.
In recent years, in a broadcasting station for producing and broadcasting television programs, an MPEG technology is generally adopted to carry out processing to compress and/or encode video data. In particular, the MPEG technology is becoming a de-facto standard for recording video data into a random-access recording medium material or a tape and transmitting video data through a cable or by way of a satellite.
The following description briefly explains typical processing carried out at a broadcasting station up to transmission of a video program produced at the broadcasting station to homes. First of all, an encoder employed in a cam-coder encodes source video data and records the encoded data onto a magnetic tape of a VTR (Video Tape Recorder). A cam-coder is an apparatus comprising a video camera and the VTR, which are integrated to form a single body. At that time, the encoder employed in the cam-coder encodes the source video data into codes with a recording format suitable for the magnetic tape of the VTR. For example, in a GOP (Group of Pictures) structure of an MPEG bit stream recorded onto the magnetic tape, 1 GOP consists of 2 picture frames. Thus, an MPEG bit stream is a sequence of picture frames such as I, B, I, B, I, B and so on where notations I and B represent picture frames with different types. An MPEG bit stream is recorded onto a magnetic tape at a bit rate of 18 Mbps.
Then, edit processing is carried out at a main broadcasting station to edit the video bit stream recorded on the magnetic tape. In order to carry out the edit processing, the GOP structure of the video bit stream recorded on the magnetic tape is converted into a GOP structure suitable for the edit processing. In a GOP structure suitable for the edit processing, 1 GOP comprises 1 frame and all pictures are I pictures. This is because, in order to carry out the edit processing in frame units, the I picture is most suitable since the I picture has no correlation with other pictures. In an actual edit operation, the video bit stream recorded on the magnetic tape is first decoded, being restored to base-band video data. Then, the base-band video signal is re-encoded so as to convert each picture into an I picture. By carrying out decoding and re-encoding processes in this way, it is possible to generate a bit stream having a GOP structure suitable for the edit processing.
Next, in order to transmit an edited video program obtained as a result of the editing described above from the main broadcasting station to a local broadcasting station, the GOP structure and the bit rate of the bit stream of the edited video program are converted into a GOP structure and a bit rate that are suitable for transmission processing. A GOP structure suitable for transmission between stations is a GOP structure in which 1 GOP consists of 15 picture frames such as I, B, B, P, B, B, P and so on where notation P represents a picture frame of a certain type different from the picture frames I and B. On the other hand, a desirable value of the bit rate suitable for transmission between stations is at least 50 Mbps. This is because a dedicated transmission line having a high transmission capacity is generally used for transmission between stations. To put it concretely, the bit stream of the video program obtained as a result of the edit processing is first decoded, being restored to base-band video data. Then, the base-band video data is re-encoded to convert the GOP structure and the bit rate of the base-band video data into a GOP structure and a bit rate that are suitable for the transmission processing.
At a local broadcasting station, edit processing is carried out to insert commercials unique to the geographical area of the local broadcasting station into the video program received from the main broadcasting station. That is to say, much like the edit processing described above, the video bit stream received from the main broadcasting station is first decoded, being restored to base-band video data. Then, the base-band video signal is re-encoded so as to convert each picture into an I picture. By carrying out decoding and encoding processes in this way, it is possible to generate a bit stream having a GOP structure suitable for the edit processing.
Next, in order to transmit an edited video program obtained as a result of the editing described above from the local broadcasting station to homes, the GOP structure and the bit rate of the bit stream of the edited video program are converted into a GOP structure and a bit rate that are suitable for transmission processing. A GOP structure suitable for transmission from a local broadcasting station to homes is a GOP structure in which 1 GOP consists of 15 picture frames such as I, B, B, P, B, B, P and so on. On the other hand, a desirable value of the bit rate suitable for transmission from a local broadcasting station to homes is about 5 Mbps. To put it concretely, the bit stream of the video program obtained as a result of the edit processing is first decoded, being restored to base-band video data. Then, the base-band video data is re-encoded to convert the GOP structure and the bit rate of the base-band video data into a GOP structure and a bit rate that are suitable for the transmission processing.
As is obvious from the above description, during transmission of a video program from the main broadcasting station to homes, decoding and encoding processes are carried out repeatedly a plurality of times. In actuality, processing carried out at a broadcasting station includes various kinds of necessary signal processing other than the signal processing described above and, for each signal processing, decoding and encoding processes must be performed.
Unfortunately, however, encoding and decoding processes based on the MPEG standard are not 100% reversible processes as is generally known. That is to say, video data obtained as a result of a decoding process is not 100% the same as base-band video data prior to an encoding process. To be more specific, the picture quality deteriorates due to the encoding and decoding processes. To put it in detail, when the encoding and decoding processes are carried out repeatedly as described above, there is raised a problem that the picture quality inevitably deteriorates each time a process is performed. In other words, each time the decoding and/or encoding processes are repeated, the picture quality deteriorates cumulatively.
In order to solve this problem, there has been proposed a technique for preventing the picture quality from deteriorating by transmission of an encoding history of transmitted video data along with the video data and execution of encoding and decoding processes by using the encoding history.
In the execution of the decoding and encoding processes, however, a transcoding system may not require all parameters in some cases in dependence on the application to process pictures. Since an area in which required data is located is not known, nevertheless, it is necessary to design such hardware that all data is accessible to the transcoding system. For this reason, the hardware becomes unavoidably complicated and, as a result, the information-processing apparatus inevitably becomes large in scale. In addition, if a packet is lost due to an effect of a noise, restoration of data including and following the lost packet becomes difficult so that it is feared that much data is unavoidably lost.